Differential effects of immobilized and free forms of phosphate-solubilizing fungal strains on the growth and phosphorus uptake of mung bean plants

This communication deals with the isolation, screening and evaluation of the phosphate solubilization activity of microorganisms to manage soil microbial communities and to select potential microbial inoculants. Thirty-two isolates were recovered from farmland soil samples of the Banasthali region, Rajasthan, India, out of which 17 showed phosphate solubilizing potential. These microorganisms were further screened on the basis of solubilization efficiency of inorganic phosphate sources in Pikovskaya agar and broth media containing tricalcium phosphate as an insoluble source of phosphorus. Two isolates, S33 and S36, demonstrating the highest phosphate solubilizing potential, and later identified as Aspergillus tubingensis and A. niger , respectively, were selected for further work. These isolates were able to solubilize other inorganic forms of P viz. dicalcium phosphate, ferric phosphate and Udaipur rock phosphate. These were further immobilized using calcium alginate and agar as carrier, to check the phosphate solubilization in vitro, and in vivo on mung bean plants grown in pots.